Cortical association areas found within the neocortex are considered to be the foundation for the complex form of behavior observed in primates / Photo by Andrea Danti via 123rf.com

Recent reports indicate that a team of scientists is now extrapolating new clues as to how human beings evolved the capacity and predisposition for speech, and they’re getting these clues from the study of other primates. Lead scientist on the project, Jacob Dunn, hails from Anglia Ruskin University as a senior lecturer, and his team focused on two main facets of the brain, one of which was examined in the neocortex. Previously established information on the neocortex in both human beings and other primates indicates that therein lie clues as to why humans are the only primates that can hold conversation and, perhaps, how that even came to be.

Some of Dunn’s team came from Stony Brook University, and together, they found a positive correlation between the sizes of primates’ vocal repertoires and the comparative sizes of cortical association areas. These areas constitute one of the main brain features on which the study concentrated, and they rest in the neocortex. These are specifically cortical association areas that regulate the control of one’s own conscious behavior. That positive correlation spans the full range of primates like pottos with fairly small cortical association areas relative to other mammals and only two kinds of vocalization versus the far larger cortical association areas in the neocortices of bonobos linked to their 38 vocalization types.

Dunn said explicitly, “This study shows, for the first time, a significant positive correlation between the vocal repertoire and the relative size of the parts of the brain responsible for voluntary control over behavior. Cortical association areas are found within the neocortex and are key to the higher cognitive processing capabilities considered to be the foundation for the complex forms of behavior observed in primates. Interestingly, the overall size of the primate’s brain was not linked to the vocal repertoire of that species, only the relative size of these specific areas.” In other words, bigger brains don’t necessarily translate to speech capability, not unless they are bigger specifically because of larger cortical association areas in the neocortex.

“We also found a positive relationship between the relative volumes of the cortical association areas and the hypoglossal nucleus in apes, both of which are significantly bigger in these species,” Dunn also adds. “The hypoglossal nucleus is associated with the cranial nerve that controls the muscles of the tongue, thus suggesting increased voluntary control over the tongue in our closest relatives. By understanding the nature of the relationship between vocal complexity and brain architecture across non-human primates, we hope we are beginning to identify some of the key elements underlying the evolution of human speech.”

It’s a groundbreaking revelation that speaks to some of the revelations of old that were less substantial in their evidence yet equally influential if not more so. Many people are familiar, though some aren’t, with what’s called Dunbar’s Number. Even for those who are familiar with it, there’s a good chance they’re familiar with a misinterpretation of the meaning of that value. The common use of the term, Dunbar’s Number, is usually used to simply describe the average number of relationships a single human being has; it’s often viewed as the average size of a human being’s social network. That’s wrong.

Dunbar’s Number is 150. It’s an estimated ceiling on how many social relationships a person can functionally sustain, which quite different. Viewing it as just how many relationships the brain can handle doesn’t take into account the fact that not all relationships are created equal and that, therefore, one doesn’t value every relationship the same. The misinterpretation then assumes a basically perfect distribution for one’s social network in which all relationships carry equal weight. The implication is supposed to be that human beings can functionally sustain—interact with semi-regularly, remembering name-and-face correlations—150 relationships at max. That would also mean that the 500 contacts in your list are mostly foddering with a maximal 150 whom you could recognize at the mall, greet affectionately at the spur of the moment with the correct name and perhaps share an anecdote or joke.

Dunbar’s Number is, of course, to be taken with a grain of salt even for those who correctly define it and use it in its proper context, but it’s based on a theory established in the early ‘90s by Robin Dunbar, a premier evolutionary psychologist for his day. His theory was that the sizes of the groups he observed animals is likely correlated with the sizes of their respective brains. The hypothesis came from the fact that interaction requires brainpower, which is a veritable reality, so he figured that socializing and bonding with multiple members of one’s species, especially retaining memories of past interactions with them, would necessitate this correlation between brain sizes and social group sizes. Dunbar, however, narrowed the scope of his theory to justify the neocortex because he realized just how integral the neocortex was to interactions, and his focus remained with primates.

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